I'm not a hater, I like the guy. However, if Chisora can throw his weight around and give him such a rough fight it doesn't bode well for him against the top Big HWs.
He is a splendid boxer who is a joy to watch. Along with his quirky personality he is ' must-see'. I think he can beat most HWs out there, except for the top tier. But I definitely want to see him try.
He's a superb HW, one of the few guys of recent years who beats opponents with pure skills regardless of size and power. Chisora is a fringe top ten fighter and Usyk outclassed him without much problem at all. He'll do the same to Parker, Whyte, Povetkin, Ruiz, Wilder, whoever you care to name outside of Juicy J and the Furious One. Only other HWs I see giving him issues are possibly Kabayel and Briedis again.
34 is getting up there for guys that fight below 147. Higher weight classes I'd say prime for the top stars is early 30's and 33-34 is still right there. Uysk has beaten Hunter and Chisora. Hunter is #4 in the IBF. Chisora is #8 in the WBC. Definitely then Uysk is Top 10 HW (factoring in also that he is undefeated) but is he championship level at HW? At 33-34 he doesn't have time to hang out in the rankings and has to take his title shot with the idea of being able to get one in the next 12-18 months. If the goal is to clean out the division, Uysk is the only undefeated guy in the Top 10 that is ready to go now. Dubois has time and can wait a few years until the current generation kings (Fury/AJ/Wilder) age out. Of course anything could happen. AJ had a massive loss and Fury quit the sport. For the above reasons I would not write Uysk's chances off. He may end up with a belt at HW but all of them depends on the stars aligning. If it comes down to AJ and Fury fighting twice and trading all the belts in 2021 is Uysk next in line for the winner? He might not be depending on contracts.
With age what you say is true but wear and tear is the big killer which I'm concerned about with someone like Usyk. Loma's troubles starting to come through. No weight cuts is a big benefit.
Uysk unifying all the belts at HW seems improbable at the moment. Even AJ is a long shot to do it. Think about the probabilities. Fury defeating Takam 95% chance Joshua defeating Puvlev 80% chance The probability of Fury/AJ fight going for all the belts in 2021 then is 76%. If you make Fury just a 2 to 1 favorite to do it that gives Fury a 50% chance to unify and AJ a 25% chance. Then if Fury got the belts he'd have to defend them in a rematch with AJ. Let's say he is favored 3 to 1 in the rematch and wins. The probability of Fury unifying and defending are only 37.5%. The chances of AJ winning both fights as a 2-1 favorite in the rematch is 16.5%. Uysk would have the best shot if Fury defeated AJ cleanly twice. At that point he has like a 1/3 chance of getting a crack at Fury after that in 18 months and Fury would be favored 5 to 1. In a best case scenario then Uysk has 2.5% chance of unifying the belts himself. Where Uysk does have good chances at since he is 17-0 and is one of the few in the Top 10 not to have fought Fury or AJ before is a title shot at some point over the next 2 to 3 years. His situation reminds me a lot of Povetkins where he hung around long enough to get a crack at AJ and may get another title shot if he beat Dillian Whyte the second one. Even if Uysk were to stumble before a shot at the title he still would have a chance if he hung around the HW division of having his name called at some point due to having a couple Top 10 HW wins on his resume, being a former unified Cruiserweight champ ect.
Usyk is Joshua's mandatory. He will press the issue after the Pulev fight. And then Joshua will have to vacate the title or defend the title against Usyk.
To add to your argument Uysk has pulled out of fights lately because of injuries, like the Takam fight last year. I still have my ticket for that one. That could delay any title shot. Povetkin however is 41 and if he wins a second time against Whyte he becomes a mandatory for another title shot. This is the heavyweight division where legs aren't as much a factor. As to Loma his two losses were to much naturally larger men. Teo's camp however things he's got upside to 147 or even 154 at some point. Loma bit off more than what he could chew more than anything else.